either be homogeneous or heterogeneous, i.e., uncatalyzed or Pulsed nuclear magnetic resonance was used to monitor the catalyzed by some impurity (5). The latter mechanism is of crystallization of supercooled liquid droplets in 30 wt% n-hexadeparticular interest, since heterogeneous nucleation may be initicane oil-in-water emulsions at 6ΠC. Crystallization was induced in ated by impurities distributed randomly throughout the bulk of the liquid droplets when solid droplets of the same material were the material (bulk heterogeneous) or by ''impurities'' at the present. The rate of induced crystallization increased as the conoil-water interface (surface heterogeneous) (4, 5). Recently, centration of free non-ionic surfactant (polyoxyethylene sorbitan it has been observed that nucleation may be induced in a supermonolaurate) in the aqueous phase increased from 0 to 14 wt%.
cooled liquid droplet if a solid droplet of the same material is Differential scanning calorimetry measurements indicated that present (5, 6). It has been proposed that such interdroplet free surfactant had no effect on crystal nucleation of individual droplets. These results indicate that the surfactant enhances in-heterogeneous nucleation occurs when a crystal protruding duced crystallization by altering colloidal interactions between from a solid droplet penetrates into a liquid droplet and acts droplets. Creaming measurements showed that flocculation was as a nucleation site for crystal growth (6).
enhanced in emulsions when the free surfactant concentration was
The rate of interdroplet nucleation has been found to deincreased. We propose that the presence of free surfactant micelles pend on the type of oil in the droplets, the chemical structure increases the attraction between droplets because of an osmotic of surfactant molecules, the droplet size, the aqueous phase effect, and this attraction facilitates the ability of solid crystals viscosity, and the concentration of free surfactant in the from one droplet to induce crystallization in an adjacent liquid aqueous phase (5-8). The nucleation rate increases as dropdroplet.